1. Field of Invention:
This invention relates to heat insulating plates and more particularly to heat insulating plates used in motor vehicles which not only provide heat insulation but also absorb vibration.
2. Prior Art:
In general heat insulating plates are disclosed around an exhaust manifold, hot air intake manifold and the like which constitute the main heat sources in a motor vehicle engine, etc., thereby reducing the damage caused by such heat sources to parts located there around.
However, it has been common practice to utilize materials having a low damping capacity such as steel as the heat insulating plate and the heat insulating plates are secured to the heat source in slightly spaced apart relationship with the outer surface of the heat source. Consequently, there has been presented a disadvantage that, with a heat source subjected to intense vibrations such as a motor vehicle engine, the heat insulating plate itself vibrates to create a new noise source and cause high resounding noise. This disadvantage is particularly noteable with a heat insulating plate of cantilever type construction which is secured to the main body of the engine as a heat insulating plate used for heat insulating of an exhaust manifold of a motor vehicle engine.
On the other hand, in order to reduce vibrations of the heat insulating plate caused by vibrations of an engine, some solutions have been suggested which include changing the weight of the heat insulating plate, adding a weight to the heat insulating plate and changing the resonant frequency of the heat insulating plate. Particularly, with a motor vehicle engine wherein the vibrational frequencies vary to a considerable extent depending upon the running conditions, it is difficult to set the resonant frequency of the heat insulating plate so as to be out of all of the vibrational frequency bands generated by the engine.
Furthermore, it has been suggested that one should utilize a vibration absorbing material such as asbestos to make a heat insulating plate as a whole instead of using a metal plate as the heat insulating plate. However, there has been a problem in that if asbestos is used as the portion heavily affected by heat from the heat source the asbestos is broken down into pieces due to the heat and therefore ceases to function as the heat insulating plate.